title: Annulus fibrosus cells interact with neuron-like cells to modulate production of growth factors and cytokines in symptomatic disc degeneration.
abstract: METHODS
  We hypothesized that AF/neuron interactions during annular injury were involved in neovascularization and nerve ingrowth, the pathologic hallmarks of symptomatic disc degeneration.
  
  
  OBJECTIVE
  To identify growth factors and inflammatory cytokines related to AF/neuron interactions using in vitro model.
  
  
  BACKGROUND
  Discogenic pain is the chronic intractable pain initiated by tears in the outer annulus fibrosus (AF); this is a unique structure with free nerve endings at outer one-third, located beside dorsal root ganglia. The relationship between AF and neuron cells in annular injury has not been extensively investigated.
  
  
  METHODS
  Human AF cells were cocultured with a retinoic acid (RA)-treated SH-SY5Y human neuroblastoma cell line (neuron-like cells). Conditioned media from cells cultured alone or in coculture were assayed for growth factors and inflammatory cytokines using enzyme-linked immunosorbent assays. The responses of the neuron-like cells, the AF cells, and the cocultured group to IL-1β/TNF-α were compared using the same outcome measures.
  
  
  RESULTS
  RA-treated SH-SY5Y cells showed significant neurite outgrowth on the 7th day; this is a typical morphologic finding of neuron-like cells. Neuron-like cells produced vascular endothelial growth factor (VEGF) and IGF-1 under basal conditions and dose-dependently secreted small amounts of IL-8 in response to TNF-α. Coculturing enhanced the secretion of VEGF, TGF-β1, and β-NGF, and suppressed the production of IGF-1. VEGF in the coculture group and the AF cells was downregulated by IL-1β/TNF-α stimulation. IL-1β/TNF-α stimulation enhanced the production of large amounts of IL-6 and IL-8 from AF cells; IL-1β produced a greater response than TNF-α. The neuron-like cells did not produce detectable amounts of IL-6 or IL-8.
  
  
  CONCLUSIONS
  These studies suggest that AF cells are involved in an inflammatory reaction and that the interactions between AF and neuron-like cells enhance the production of growth factors responsible for neovascularization and nerve ingrowth. AF injury has the potential to initiate neovascularization/nerve ingrowth and an inflammatory reaction through the interactions of AF and neural tissues.
authors.affiliation: Department of Neurosurgery, College of Medicine, Korea University, Seoul, Korea.
authors.forename: Hong Joo
authors.initials: HJ
authors.lastname: Moon
authors.forename: Joo Han
authors.initials: JH
authors.lastname: Kim
authors.forename: Hack Sun
authors.initials: HS
authors.lastname: Lee
authors.forename: Silky
authors.initials: S
authors.lastname: Chotai
authors.forename: James D
authors.initials: JD
authors.lastname: Kang
authors.forename: Jung Keun
authors.initials: JK
authors.lastname: Suh
authors.forename: Youn-Kwan
authors.initials: YK
authors.lastname: Park
mesh_terms: D045744:Cell Line, Tumor; D018920:Coculture Techniques; D017077:Culture Media, Conditioned / Q000737:chemistry; D016207:Cytokines / Q000378:metabolism*; D005260:Female; D006801:Humans; D053583:Interleukin-1beta / Q000494:pharmacology; D007403:Intervertebral Disc; D055959:Intervertebral Disc Degeneration; D008297:Male; D009389:Neovascularization, Pathologic / Q000139:chemically induced; D009414:Nerve Growth Factors / Q000378:metabolism*; D016501:Neurites / Q000187:drug effects / Q000473:pathology; D009447:Neuroblastoma / Q000378:metabolism / Q000473:pathology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D011994:Recombinant Proteins; D014212:Tretinoin / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D017077:Culture Media, Conditioned; D016207:Cytokines; D053583:Interleukin-1beta; D009414:Nerve Growth Factors; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D014212:Tretinoin